In the fields of molecular biology and biochemistry, biopolymers such as nucleic acids and proteins from organisms are identified and fractionated in order to search useful genes or to diagnose diseases. As a pre-treatment of such identification and fractionation, a hybridization reaction is often employed in which a target molecule in a sample is hybridized with a nucleic acid or a protein of a known sequence. However, when this method is employed for analyzing a hereditary disease, for example, it is troublesome and time-consuming to identify the disease since about 3,000 hereditary diseases are currently known. The currently proceeding human genome projects aim at analyzing all of human genomes which presumably total several hundred thousands of bases. Obviously, it is very time-consuming and troublesome if this is to be conducted completely in manual.
On the other hand, devices have been developed which are capable of processing a mass of sample in a short time. One example of such device is described in "Rapid genetic sequence analysis using a DNA probe array system: Thane Kreiner, Affimetrix, Inc., (American Laboratory, 1996 March, pp.39-43)". This analyzer uses a biochip 100 shown in FIG. 10 which is provided with a plurality of features 101 arranged in matrix on the surface thereof. The features 101 are immobilized with various kinds of probes. The biochip 100 is placed in a reaction vessel called a chamber together with sample DNA such that the sample DNA labeled with fluorescence hybridizes with the probes bound to the features 101 of the biochip 100. Then, the biochip 100 is irradiated with excitation light, thereby detecting a fluorescence intensity at each feature 101 to determine an amount of binding between each probe and the sample DNA. The result can be used as advantageous information.
In the case of the above-described device, the biochip 100 bound with probes is placed in the reaction vessel. The sample DNA or other reagent in a sample or a reagent container is injected into the reaction vessel through a tube by a peristaltic pump, whereby the biochip 100 is partially immersed in the sample or the reagent injected into the reaction vessel. The sample DNA or the reagent in the reaction vessel is spread or applied to the entire features 101 by shaking the reaction vessel.
However, the above-described way of applying the sample to all of the probe-bound features 101 of the biochip 100 requires a large amount of sample. For example, in the case of a biochip with an area of 1.28 cm.times.1.28 cm (i.e., 1.64 cm.sup.2), the chamber needs to be filled with a sample of 350 .mu.l to perform a single hybridization reaction. Considering the fact that the sample from the sample container is introduced into the reaction vessel via the tube, the actual amount of the sample required will increase by several times. In addition, there is also a need of washing an excessive amount of the sample away. Reaction errors caused by varying amounts of sample applications among the features 101 have been responsible for low reliability of the reaction vessel. In order to prevent such errors, an even amount of the sample needs to be applied to the entire features 101.
The present invention was accomplished in view of the above prior art problems, and aims at providing a sample application method and device wherein a sample is evenly applied over entire features of a biochip with a less amount of the sample.
The term "sample" as used with the present invention, refers not only to a sample collected from an analyte but also to various reagents. Specifically, the term "sample" as used herein includes any fluids applied to the features of the biochip, such as a buffer solution containing sample DNA or a reagent used for PCR (Polymerase Chain Reaction).